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Old 09-02-2017, 07:51   #1
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Using a relay with a new Simrad autopilot

Just purchased a new Simrad AP and in the installation process. So far mostly very straightforward but have generated one question.

Simrad (and their twin B&G) recommends using an isolating relay to engage the electric clutch (or also the hydraulic solenoid if you have a hydraulic drive) when using a non Simrad drive unit. Since I have a perfectly good, functioning and (even better) properly installed Raymarine linear mechanical drive I see no reason for now to change. Since the clutch in the Ray drive probably draws no more than the similar clutches or solenoids that engage the Simrad drives why the isolating relay? My guess it's a CYA issue for just in case.

So the question, what relay? Obviously for the AP I would want something bulletproof reliable. Standard mechanical relays do seem to work just fine in cars and other applications and run for years but would a solid state relay be better or worse? Any one have any suggestions or preferences? Power draw would be minimal. Haven't found that spec yet for the clutch on the Ray drive but should be well under an amp.
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Old 09-02-2017, 21:57   #2
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Re: Using a relay with a new Simrad autopilot

Lecomble and Schmitt have what they call an Eco-pilot or electro-valve that they claim reduces the Ah usage dramatically. I'm sure there are other sources for these energy efficient relays.
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Old 09-02-2017, 22:39   #3
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Re: Using a relay with a new Simrad autopilot

I think you answered your own question on why it's needed.... so why bother with it.
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Old 10-02-2017, 02:31   #4
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Re: Using a relay with a new Simrad autopilot

Most solid state relays are for switching AC so good luck finding a DC switching unit at the right price. As to whether you need one or not, it basically boils down to the current the autopilot control can provide versus the current the load draws. If the load draws less than the maximum you're almost good to go, One thing that you need to be aware of is the flyback voltage from inductive coils (as used in electromagnetic switches of all types) when the power is switched off. This can be up to 10 times the supply voltage. The usual fix is to place a diode across the load in reverse that will short this flyback voltage (it's always the reverse polarity of the supply voltage). A diode used in this situation is referred to as a "flywheel diode".

Now back to the DC solid state relay. If you really do need to switch the load because the supply doesn't have enough oomph, the easiest solution if you don't want to use a traditional relay- and because you don't actually need the isolation feature that said relay or SSR has - is to use a basic transistor circuit to perform this function. I bet there are a zillion circuits on the internet and they are basic enough that even a rank novice should be able to construct one without too much trouble. I'd also bet there's off the shelf assemblies available too for 12 Vollt and 24 volt circuits.

Good luck, I think I need to do something like this this with my A/P motor, too.
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Old 10-02-2017, 05:23   #5
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Re: Using a relay with a new Simrad autopilot

Quote:
Originally Posted by DeepFrz View Post
Lecomble and Schmitt have what they call an Eco-pilot or electro-valve that they claim reduces the Ah usage dramatically. I'm sure there are other sources for these energy efficient relays.
Did a quick look at this and looks like it's worth checking out closer. Since the power for the AP clutch is constant, even though small compared to the instantaneous power draws of the motor, the total daily draw does add up. If this unit works with my drive could be a good option, even if as I suspect, I really don't need an isolating relay to "protect" the Simrad engaging output circuit.

Thanks
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Old 10-02-2017, 05:26   #6
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Re: Using a relay with a new Simrad autopilot

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Originally Posted by smac999 View Post
I think you answered your own question on why it's needed.... so why bother with it.
I did do an initial test at the mooring and the Ray drive engaged just fine connecting directly to the Simrad unit so I agree it's probably not really needed. So unless the Ecopilot mentioned by Deepfrz does offer a power savings I'm very tempted to forget the relay.
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Old 10-02-2017, 05:40   #7
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Re: Using a relay with a new Simrad autopilot

Quote:
Originally Posted by Reefmagnet View Post
Most solid state relays are for switching AC so good luck finding a DC switching unit at the right price. As to whether you need one or not, it basically boils down to the current the autopilot control can provide versus the current the load draws. If the load draws less than the maximum you're almost good to go, One thing that you need to be aware of is the flyback voltage from inductive coils (as used in electromagnetic switches of all types) when the power is switched off. This can be up to 10 times the supply voltage. The usual fix is to place a diode across the load in reverse that will short this flyback voltage (it's always the reverse polarity of the supply voltage). A diode used in this situation is referred to as a "flywheel diode".

Now back to the DC solid state relay. If you really do need to switch the load because the supply doesn't have enough oomph, the easiest solution if you don't want to use a traditional relay- and because you don't actually need the isolation feature that said relay or SSR has - is to use a basic transistor circuit to perform this function. I bet there are a zillion circuits on the internet and they are basic enough that even a rank novice should be able to construct one without too much trouble. I'd also bet there's off the shelf assemblies available too for 12 Vollt and 24 volt circuits.

Good luck, I think I need to do something like this this with my A/P motor, too.
Thanks for the information on solid state relays. Even though I have an EE background obviously I have no practical knowledge of those devices beyond an awareness that they exist.

I have not been able to find the specs for the power draw of the clutch in the Raymarine drive. Maybe the next step is to contact them to see if I can get that bit of info or just give up and measure the current the clutch actually draws when engaged.

Regarding the diode to block the reverse voltage spike, since the output from the Simrad is specifically for engaging an AP drive clutch or solenoid operated hydraulic valve (but only "certified" for their brand name drives) one might assume that this problem was addressed in the internal circuit design and may have a diode or reverse voltage protection circuit of some type built in. But we all know what assumptions can get you.

And yes I could probably build a little circuit to accomplish this and probably even have the bits in my shop but at this point I am so overwhelmed with work and house projects and boat projects and family stuff (new granddaughter so this is a good thing to have on my plate) that off the shelf, if it saves me an hour of reading and building, is worth it.
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Old 10-02-2017, 06:12   #8
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Re: Using a relay with a new Simrad autopilot

Quote:
Originally Posted by skipmac View Post
Did a quick look at this and looks like it's worth checking out closer. Since the power for the AP clutch is constant, even though small compared to the instantaneous power draws of the motor, the total daily draw does add up. If this unit works with my drive could be a good option, even if as I suspect, I really don't need an isolating relay to "protect" the Simrad engaging output circuit.

Thanks
Is your Raymarine a hydraulic or mechanical linear drive...most Raymarine's are not hydraulic. The clutch in the mechanical drives requires continuous/constant power and is not a solenoid like in the hydraulic units. Good news is, since they are more efficient than a hydraulic unit, you're already ahead.

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Old 10-02-2017, 06:20   #9
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Re: Using a relay with a new Simrad autopilot

While I haven't tried it out yet, I installed a device that lowers the power to the solenoid by a factor of nine after 300 milliseconds. Supposedly, this is the threshold of power needed to hold the solenoid in place after engagement.

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Old 10-02-2017, 06:39   #10
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Re: Using a relay with a new Simrad autopilot

Quote:
Originally Posted by funjohnson View Post
Is your Raymarine a hydraulic or mechanical linear drive...most Raymarine's are not hydraulic. The clutch in the mechanical drives requires continuous/constant power and is not a solenoid like in the hydraulic units. Good news is, since they are more efficient than a hydraulic unit, you're already ahead.

Matt
The drive is a mechanical linear and yes, I do believe it's more efficient than the hydraulics.

Since the clutch is electrically operated I assume it is electro magnetic which indicates a coil to create the magnetic field which I think technically qualifies as a solenoid. Yes I know, nit picky aren't I?

As noted, in some areas my electrical knowledge is more theoretical than hands on. I do clearly understand that a clutch needs constant power to stay engaged (which as I mentioned, adds noticeably to the total power usage of the AP). So, assuming the clutch in the mechanical linear drive does indeed have a coil to engage it, I'm wondering if the power to maintain this is lower than the power to initiate it and I could then use the Ecopilot to save some power.

I did find the specs for that online and price, $192 list ouch.
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Old 10-02-2017, 06:43   #11
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Re: Using a relay with a new Simrad autopilot

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Originally Posted by funjohnson View Post
While I haven't tried it out yet, I installed a device that lowers the power to the solenoid by a factor of nine after 300 milliseconds. Supposedly, this is the threshold of power needed to hold the solenoid in place after engagement.

Matt
Sounds like the L & S Ecopilot which is a bit pricey. What are you using? Cost?
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Old 10-02-2017, 07:14   #12
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Re: Using a relay with a new Simrad autopilot

Look at the hydraulic solenoid coil drivers, there are several out there with energy / coil saving functions:
ELACTIS - Solenoid Valve and Solenoid Power Saving Electronics in DIN 43650 Connectors
or look up nass magnet, like this one
Solenoid valve Electrical Connector Form A with 11-89% Energy Saving
or the hot-shot coil saver
http://www.axiomatic.com/TD2100AX.pdf

Dirk
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Old 10-02-2017, 07:17   #13
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Re: Using a relay with a new Simrad autopilot

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Sounds like the L & S Ecopilot which is a bit pricey. What are you using? Cost?
Very similar, but a little high power drop. A swedish acquaintance who makes hydraulic computer control systems made it for me.... free. Here the spare in all its glory Click image for larger version

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Old 10-02-2017, 08:38   #14
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Re: Using a relay with a new Simrad autopilot

Simrad does not know which drive of another brand will be installed, I think that is why they recommend the relay.
As for the consumption it is easy to know if you need a relay or not, reading in the Navico manuals the maximum output power for the clutch and the manual of the drive its consumption.
Another problem may be the return voltage when switching off a solenoid.
Depending on the configuration of the solineoid, even small can reach thousands of volts with reverse polarity.
This can also be solved with a diode connected in parallel with the solenoid that makes the energy circulate through the solenoid and dissipate.
I would put an automotive relay mounted in a socket for easy exchange and leave one or two on board for exchange. It is very cheap.
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Old 10-02-2017, 09:05   #15
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Re: Using a relay with a new Simrad autopilot

Obrigado Dieter,

Quote:
Originally Posted by dietervoegeli View Post
Simrad does not know which drive of another brand will be installed, I think that is why they recommend the relay.

Exactly. Since there are many, many different drive units and configurations it would be very difficult for Simrad to make recommendations for all the possible options. The safest thing for Simrad then is to recommend the isolating relay.

As for the consumption it is easy to know if you need a relay or not, reading in the Navico manuals the maximum output power for the clutch and the manual of the drive its consumption.

I easily found the output capacity for the Simrad AP unit but have not yet been able to get the power requirement for the clutch circuit in the Raymarine drive. The only specifications in any of the Raymarine documentation is average total power consumption. Does not break that spec down to power to the clutch and power to the motor or even max power used by the motor. Not very helpful.

Another problem may be the return voltage when switching off a solenoid.
Depending on the configuration of the solineoid, even small can reach thousands of volts with reverse polarity.
This can also be solved with a diode connected in parallel with the solenoid that makes the energy circulate through the solenoid and dissipate.
I would put an automotive relay mounted in a socket for easy exchange and leave one or two on board for exchange. It is very cheap.

Using a standard automotive relay is an idea I am considering. As you say, they are cheap and they are pretty reliable. Relays designed to go around the engine, under the hood are also somewhat weather resistant. I do like your suggestion to install a socket for quick replacement. That would be a quick, easy solution for any repairs.
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